1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a fabrication method of a gate electrode having a dual gate insulating film.
2. Discussion of the Related Art
A conventional fabrication method of a gate electrode having a dual gate insulating film will be described with reference to the accompanying drawings.
FIGS. 1A-1E are cross-sectional diagrams sequentially illustrating a conventional fabrication method of the gate electrode having the dual gate insulating film.
As shown in FIG. 1A, a first insulating film (gate insulating film) 2 is formed on a semiconductor substrate 1 having a first portion 1a and a second portion 1b, and a photoresist film 3 is formed thereon. The first insulating film 2 is a silicon oxide film and is usually formed by a thermal oxidation process. A thickness of gate insulating films to be formed on the first and the second portions 1a, 1b may be different from each other.
As shown in FIG. 1B, the photoresist film 3 is etched and patterned to expose the first insulating film 2 corresponding to the second portion 1b of the substrate 1. Therefore, a photoresist film 3a is formed.
Next, as shown in FIG. 1C, in order to expose the second portion 1b of the semiconductor substrate 1, the first insulating film 2 is etched and patterned using the photoresist pattern 3a as a mask. Therefore, a first insulating film pattern 2a is formed, and the photoresist pattern 3a is then removed by a wet-dip process, wherein the semiconductor substrate 1 including the first insulating film pattern 2a and the photoresist pattern 3a is dipped into an etching solution and then taken out.
As shown in FIG. 1D, a second insulating film 4 (gate insulating film) is formed on the semiconductor substrate 1 having the first insulating film pattern 2a, and a conductive film 5 is formed on the second insulating film 4. The second insulating film 4 is a silicon oxide film and is usually formed by a thermal oxidation process, and the conductive film 5 is a polysilicon film and is usually formed by a chemical vapor deposition (CVD).
As shown in FIG. 1E, a gate electrode 6 is respectively formed on the first and the second portions 1a, 1b of the semiconductor substrate 1 by patterning the conductive film 5. A thickness of the gate insulating film of the first portion 1a is thicker than that of the second portion 1b.
According to the conventional method, the gate insulating film is often contaminated by infiltrating through a diffusion for metallic and carbonaceous elements of the photoresist film when the gate insulating film is etched and patterned using the photoresist film as a mask, and is easily damaged because it is difficult to control etched volume of the photoresist film. Therefore, the gate insulating film may not have uniform thickness, reducing reliability of the semiconductor device.